xHCI: use gfp flags from caller instead of GFP_ATOMIC

The caller is allowed to specify the GFP flags for these functions.
We should prefer their flags unless we have good reason.  For
example, if we take a spin_lock ourselves we'd need to use
GFP_ATOMIC.  But in this case it's safe to use the callers GFP
flags.

The callers all pass GFP_ATOMIC here, so this change doesn't affect
how the kernel behaves but we may add other callers later and this
is a cleanup.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>